In recent years, demand for a battery such as a lithium ion battery has been increasing in a variety of applications such as a domestic small power storage device, an electric motorcycle, an electric vehicle, and a hybrid electric vehicle in addition to a portable terminal such as a portable information terminal or a portable electronic device.
With spread of the applications, further improvement of safety of the battery is required. In order to ensure safety, a method for preventing liquid leakage, and a method using a solid electrolyte in place of a combustible organic solvent electrolyte are useful.
As the solid electrolyte, a polymer solid electrolyte using polyethylene oxide or the like is known (Patent Literature 1). However, the polymer solid electrolyte is a combustible material. In addition, as the solid electrolyte, an inorganic solid electrolyte formed of an inorganic material has been also proposed (Patent Literature 2 or the like). An inorganic solid electrolyte is a solid electrolyte formed of an inorganic substance and is a non-combustible material as compared with a polymer solid electrolyte, and has very high safety as compared with an organic solvent electrolyte usually used. As described in Patent Literature 2, development of an all-solid-state battery with high safety using an inorganic solid electrolyte is progressing.
An all-solid-state battery includes an inorganic solid electrolyte layer as an electrolyte layer between a positive electrode and a negative electrode. Patent Literatures 3 and 4 describe an all-solid-state lithium secondary battery having a solid electrolyte layer formed by a method for applying a solid electrolyte layer slurry composition containing solid electrolyte particles and a solvent onto a positive electrode or a negative electrode and drying the composition (application method). In a case where an electrode or an electrolyte layer is formed by the application method, the viscosity or the fluidity of a slurry composition containing an active material or an electrolyte needs to be within a range of conditions making application possible. Meanwhile, it is important for an electrode and an electrolyte layer formed by applying a slurry composition and then drying a solvent to include an additive other than an active material and an electrolyte, such as a binder in order to exhibit characteristics as a battery. Therefore, Patent Literature 5 has proposed use of an acrylate-based polymer for a binder.